The present invention pertains to evaporative cooling systems and, more particularly, to an evaporative cooler for cooling process fluid in a closed system.
Closed loop evaporative coolers for cooling process water or other fluids in industrial applications are well known in the art. Such units are usually mounted outside the factory building, typically on a roof, where process fluid used to cool industrial equipment and machines inside the factory is directed for cooling and returned for recirculation through the equipment. In a typical evaporative cooler, a number of vertically spaced horizontally disposed banks or tiers of cooling coils are supported within a housing through which a flow of outside ambient air is induced with a fan or fans to direct cooling air into the housing and up through the tiers of coils. A spray water system, including a header and nozzle arrangement, is positioned above the uppermost tier of the main cooling coils within the housing to direct a spray of water downwardly over the coils and counter to the upward flow of cooling air. The evaporative effect of the spray water supplements the effect of the cooling air flow, all in a well known manner, to cool the process water or other cooling fluid which is continuously pumped through the serially connected banks of cooling coils.
In the use of evaporative coolers in temperate climates where operation at below freezing temperatures in winter months is required, steps must be taken to prevent freeze up of the spray water system, including the prevention of freezing in the spray water sump at the bottom of the unit where the spray water is collected and recirculated by pump to the spray header. Electric heaters or other types of heating equipment must be placed in the spray water sump to prevent freeze up in cold weather. Such heating systems add substantially to the operating costs of an evaporative cooler and, in extremely cold weather, spray water passing through the cooling coils still freezes and results in decreasing operating efficiencies. Also, the operation of spray water systems in evaporative coolers in a range of ambient temperature conditions both below and above zero often results in a characteristic formation of a plume of water vapor which is aesthetically undesirable.
It is known in the prior art to position precooling coils above the spray water header and connect the same in series with the main cooling coils in the condenser unit for a refrigeration system. U.S. Pat. No. 2,068,478 shows one such system. However, operation of the evaporative cooler includes continuous operation of the spray water system and, in addition, the precooling coils are substantially larger in size and in basic cooling capacity than are the main evaporative cooling coils.
U.S. Pat. No. 3,026,690 shows a similar system, but with a modification wherein the precooler coils and the main evaporative cooler coils though serially connected are positioned in parallel passages within the cooler housing. Thus, the precooler coils are not positioned above the spray water header so as to receive the same flow of cooling air as the main cooling coils.
U.S. Pat. No. 2,213,622 discloses an evaporative cooling unit which includes a precooling coil positioned within the cooler housing and in the flow of cooling air. The precooling coil is located immediately above the spray water header. The system includes a temperature responsive control which operates to shut off the flow of spray water as the temperature drops below freezing.
British patent specification 845844 also discloses a supplemental finned precooler positioned in the housing of an evaporative cooler above the spray water cooling system. One of the functions of the fins of the precooling coils is to act as a mist eliminator by trapping airborne spray water particles to separate the water from the cooling air discharged from the unit.